Python retry using the tenacity module

Question

I'm having having difficulty getting the tenacity library to work as expected. The retry in the following test doesn't trigger at all. I would expect a retry every 5 seconds and for the log file to reflect the retry attempts.

import paramiko
import tenacity
from configparser import RawConfigParser
import logging

def main():
    parser = RawConfigParser()
    parser.read('config.ini')
    HOST = parser['SSH']['host']
    PORT = parser['SSH']['port']
    USER = parser['SSH']['user']
    LOG_LEVEL = parser['Logging']['level']
    LOG_FILE = parser['Files']['log_file']
    LOG_FORMAT = parser['Logging']['format']

    with open(LOG_FILE, "a") as f:
        logging.basicConfig(filename=LOG_FILE,level=LOG_LEVEL,format=LOG_FORMAT)
        logging.info("******Started logging******")

    client = paramiko.SSHClient()
    client.set_missing_host_key_policy(paramiko.AutoAddPolicy())

    @tenacity.retry(wait=tenacity.wait_fixed(5))
    def connect():
        try:
            client.connect(HOST, int(PORT), USER)
            logging.info("Successful connection to remote server")
        except Exception:
            logging.error("Cannot connect to remote server")

    connect()

if __name__ == "__main__":
    main()

The log file spits this out:

> 2017-11-04 19:55:20,695 ******Started logging******
> 2017-11-04 19:55:20,695 Cannot connect to remote server

Answer 1

I suppose that tenacity detects failures by handling exceptions. In your code the exception is logged and then discarded. So, for tenacity, your call is actually successful. You should re-raise this exception to get the expected behavior. Like this:

@tenacity.retry(wait=tenacity.wait_fixed(5))
def connect():
    try:
        client.connect(HOST, int(PORT), USER)
        logging.info("Successful connection to remote server")
    except Exception:
        logging.error("Cannot connect to remote server")
        raise